Can’t do something for toffee
Definition 1 of 1
Pro Tip 1/3British Slang
This phrase is British English slang and might not be understood internationally. 
You'll find that Ellie can't dance for toffee, but she has a great time trying.
Pro Tip 2/3Humorous Tone
It's often used in a humorous or light-hearted way to describe someone's lack of skill. 
He can't cook for toffee, so we might need to order takeout.
Pro Tip 3/3Not Insulting
Although it points out a shortcoming, it's usually not meant to be an insult. 
My sister can't sing for toffee, but everyone loves her energy on stage.